This invention relates to a fuel control and feed system for an internal combustion engine and more particularly to an improved emission control system for an internal combustion engine and particularly one fueled at least in part by a gaseous fuel.
The quest for developing internal combustion engines which can operate on fossil fuels and still preserve not only natural resources but protect the economy from pollution are well known. One way in which these goals can be accomplished is to power an internal combustion engine by a gaseous fuel stored under pressure as a liquid (LPG). Such gaseous fuels tend to burn cleaner than liquid hydrocarbons such as gasoline and hence prolong engine life and increase service intervals, particularly oil change intervals. In addition, these fuels give rise to the possibility of improved emission control for a number of reasons.
Previously it has been proposed to employ as a charge former for such gaseous fuels, a generally conventional type of carburetor having a fixed venturi section into which the main fuel circuit discharges. However, there is specific disadvantage with this type of system. Conventionally, the fixed venturi section cooperates with a fuel discharge circuit in which metering jets are employed for metering the amount of fuel and air blended at the main fuel discharge. However, the amount of fuel discharge will be depend upon the air flow through the venturi section and a fixed metering jet for both air and fuel will not, under all instances give the desired control over air/fuel ratio.
It is, therefore, a principal object of this invention to provide an improved carburetor and fuel flow system for a gaseous fueled engine.
It is a further object of this invention to provide a so-called "constant depression" or "air valve" carburetor that is designed to operate on a gaseous fuel.
Although it has been proposed to employ gaseous fuel for engines having air valve type of carburetors, these systems have not been completely successful in controlling and providing the desired air/fuel ratio under all running conditions. Particularly, in the transition from idle to off/idle gaseous fueled air valve carburetors have had a difficulty in maintaining the desired air/fuel ratio.
It is, therefore, a further object of this invention to provide an improved gaseous fueled carburetor for an internal combustion engine.
It is a further object of this invention to provide an improved gaseous fueled air valve carburetor for an internal combustion engine that embodies an idle circuit for improving the control of fuel/air ratio during the transition from idle to off/idle conditions and for handling variations in running conditions even during idle.
It should be readily apparent that in order to provide good emission control as well as good fuel economy, it is essential to provide a very accurate control of the fuel/air ratio. This is normally done by controlling the amount of fuel that is supplied to the engine. At times either fixed or variable air bleeds may be employed in the fuel discharge circuit, these concepts being normally applied to liquid fueled engines.
With a gaseous fueled engine, it is the normal practice to regulate the pressure of the fuel that is delivered from a source in which it is contained under pressure as a liquid to a pressure in which the fuel becomes gaseous and at which it is at or slightly above atmospheric pressure. Normally these systems include fuel and air controls that have fixed settings or which employ metering jets or metering rods that provide a variable setting dependent upon an engine condition such as intake manifold vacuum, throttle valve position or the like. However, such controls do not always provide adequate and immediate control of the air/fuel ratio of the engine.
It is, therefore, a still further object of this invention to provide an improved charge forming system wherein the amount of fuel supplied to the engine is varied by varying the amount of air that is bled to a fuel discharge circuit of the engine in response to sensed engine operating conditions.
It is a further object of this invention to provide an improved exhaust controlled air bleed system for a gaseous fueled engine to maintain the desired air/fuel ratio under all conditions.
Normally the fuel/air ratio of an engine is controlled by using some form of sensor in the engine that will sense either air/fuel ratio directly or oxygen content in the exhaust gases to arrive at a determination of a air/fuel ratio. These types of system are so-called "feedback" control systems in that the resultant output of the engine is sensed and measured and this sensed output signal is then fed back to the fuel system to control the air/fuel ratio. Such systems can be highly effective, if the sensor provides an accurate indication of air/fuel ratio.
However, one of the most critical time periods in engine emission control is during start-up. During start-up the sensor, which may not operate below certain temperatures, cannot be relied upon to provide the initial control during starting and cold warm-up. As a result, it is very difficult with conventional engines to maintain accurate fuel/air ratios under these starting and warm-up conditions.
It is, therefore, a still further object of this invention to provide an improved control system that permits the control of air/fuel ratio during starting and warm-up.
It is a further object of this invention to provide an arrangement for quickly assuring that the sensor is in the appropriate condition to provide an accurate signal and thereafter immediately initiating air/fuel control by the sensor.
In addition to the problems as aforenoted with sensors for air/fuel ratio control, many exhaust systems employ catalytic converters for treating the exhaust gases to render certain pollutants more acceptable in order to reduce them. As is well known, many of these catalytic converters also require operation at an elevated temperature. Hence, these converters are not effective during cold starting and cold warm-up and, therefore, the exhaust emission control problems are further magnified.
Added to these difficulties is the fact that liquid fuel tends to condense out in the induction system of a conventional internal combustion engine during start-up at low temperatures and during running at low temperatures. In order to accommodate this condition, it has been the practice to supply a richer air/fuel mixture under cold starting and cold warm-up. This not only adversely effects the fuel economy, but also can have serious effects on exhaust emission control.
It is, therefore, a still further object of this invention to provide a system for an internal combustion engine having a catalytic converter wherein the converter can be rapidly heated during cold start and warm-up without requiring overly rich fuel/air mixtures.
It is a further object of this invention to provide an arrangement wherein a gaseous fuel may be employed during engine start-up to heat the catalytic converter quickly to its operating temperature.